\begin{tikzpicture}[scale=0.8]
\draw (1,1) node[below left]{$A$} -- (1,5) node[above left]{$D$} -- (7,5)
node[above right]{$C$} -- (7,1) node[below right]{$B$} -- cycle;

\draw[<-] (4,5) -- (7,5);
\draw (4,1) node[below] {$\ud x$};
\draw (7,3) node[right] {$\ud y$};

\draw[->] (0,0) -- (9,0) node[right] {$x$};
\draw[->] (0,0) -- (0,6) node[right] {$y$};

\end{tikzpicture}
